Answer: Agent Orange
Explanation: agent orange was a chemical that would burn the leaves off of the trees in Vietnam in order for the American forces (and planes) to see the Vietnamese soldiers better (and I'm pretty sure agent orange caused cancer as well)
Applied principles of physics to make practical inventions
By actually having it in a credit card so nobody except you will know the number to so nobody hacks it or it can be in your bank and nobody will get your savings
